Prolactin Assay Interference by Macroprolactin

Macroprolactinemia is a common presentation especially in gynecology and fertility clinics. However, with this clinical condition, there is a potential for misdiagnosis and unnecessary investigations/treatments due to lack of awareness of its prevalence and diagnostic approaches amongst trainees and physicians.

In this paper, we discuss the causes of hyperprolactinemia, its pathobiology, and an approach to macro-prolactinemia including relevant clinical chemistry methods and their limitations through the case of a 45-year-old female with a history of irregular menstrual cycles, who was seen in the endocrine clinic.

Patient did not have a history of infertility, galactorrhea, visual-disturbance, or headaches. Her physical examination and routine clinical chemistry investigations were unremarkable. Her initial prolactin level was 4,836 mIU/L (109 - 557) with subsequent results demonstrating diminishing levels of prolactin a month apart (1,023 mIU/L). Polyethylene glycol (PEG) precipitation test demonstrated the presence of macroprolactin with a 3% post-PEG recovery of prolactin and 111 mIU/L post-PEG prolactin concentration.

Patient's post-PRL results and clinical course confirmed the presence of macroprolactin to be the cause of factitious hyperprolactinemia. A sound approach to macroprolactinemia is critical in clinical and laboratory practices.